       (tick-clock-millis!) ; This makes 1000 msg/"second" the upper bound of throughput.
       (world-do-async-processing world)
       (-> world
-          (assoc :message-envelopes (concatv message-envelopes new-message-envelopes))
+          (assoc :message-envelopes (util/concatv message-envelopes new-message-envelopes))
           (assoc-in [:network destination-node-id] new-destination-node)))))
 
 (s/defn world-do-all-comms :- WorldSchema

  [base-duration agitation-distance]
  (let [agitation (- (*rand* agitation-distance) (/ agitation-distance 2))]
    (int (+ base-duration agitation))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(defn- concatv [coll & colls]
  (vec (apply concat coll colls)))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Schema definitions

  messages added."
  [world :- WorldSchema
   new-messages :- [MessageEnvelopeSchema]]
  (update-in world [:message-envelopes] util/concatv new-messages))

(s/defn get-node-from-world :- NetworkedNodeSchema
  [world :- WorldSchema
